Based on an idea by Carduus, I’ve made a small prototype of a pixel perfect drawing algorithm.
With Photoshop or similar tool, when you paint using the Brush/Pencil tool, you get this kind of ugly line:
Here what can be done with some tricks:
Here is a demo (maintain left click to paint). It lacks support for some special cases like drawing a line that crosses itself, but you get the idea.
Maybe it would be a nice idea to create a pixel painting software based on this? What do you think?